Medical Microbiology

Corynebacterium,Actinomyces,OtherGram-PositiveRodBacteria 255

actinomycosis,causedbyoralcavitycolonizerA.israelii,isthemostfrequent

formofactinomycosis.Treatmentincludessurgicalproceduresandantibiosis

withaminopenicillins. &

ThegroupofGram-positive,irregular(pleomorphic),nonsporingrodbacteria

includesmanydifferentgenerathatarenormalcomponentsoftheskinand

mucosalflora(Table4. 3 ,p. 26 1).Pathogensinthisgroupcausetwocharac-

teristicdiseases:diphtheria,causedbyCorynebacteriumdiphtheriaeandac-

tinomycosis,causedmainlybyActinomycesisraelii.

Corynebacteriumdiphtheriae(Diphtheria)...........

Morphologyandculturing.DiphtheriabacteriaareGram-positive,pleo-

morphic,oftenclub-shapedrods.TheindividualcellstendtogroupinV,

Y,orpalisadearrangements(Fig.4. 9 ).Neisserstainingrevealsthepolar

bodies(polyphosphatesstoredatoneendoftherod).

Lo ̈fflernutrientmedium,whichconsistsofcoagulatedserumandnutrient

broth,isstillusedfortheprimarycultures.Selectiveindicatormediumscon-

tainingtelluriteareusedinselectiveculturing.Ktelluriteisusedtoinhibit

theaccompanyingflora.TheKtelluriteisalsoreducedtotellurium,coloring

thecoloniesabrownishblack.

Extracellulartoxin.Diphtheriatoxinconsistsoftwofunctionallydistinct

fragments,AandB,wherebyBstandsforbindingtoreceptorsoftargetcells

andAstandsfortoxicactivity.FragmentAirreversiblyblocksproteinsynthe-

sistranslationinthetargetcells,whichthendie.Thetoxingeneisalwaysa

prophagegenomecomponent(seelysogenicconversion,p. 1 86).

Corynebacteriumdiphtheriae

Fig.4. 9 Gramstainingof

awoundsecretionprepara-

tioninwounddiphtheria:

typical configuration of

Gram-positiverodsofirre-

gularthickness,oftenwith

aclublikeenlargementat

oneend.

4

Kayser, Medical Microbiology © 2005 Thieme